The present invention relates to an exhaust system of a motorcycle.
In a known four-stroke-cycle multiple cylinder engine, a plurality of exhaust pipes are bundled in one unit or assembly by means of manifolds, which is then connected to a silencer. In a motorcycle, a manifold is generally disposed at a lower portion of a crank case of an engine for ensuring a large bank angle.
An engine mounted to a vehicle such as motorcycle is provided with a lot of sliding portions or rotating portions therein, and accordingly, it is necessary to be incorporated with a lubrication device for supplying a lubrication oil to reduce friction resistance of the respective portions to thereby fully achieve the suitable function of the engine.
For example, in the case of using a lubrication device of a four-stroke-cycle engine adopting a wet-sump system, the lubrication oil generally circulates such that the lubrication oil stored in an oil pan disposed at a lower portion of the crank case of the engine is pumped up by an oil pump, then filtered through an oil filter, circulates through an oil passage formed in the crank case and is then fed to various portions to be lubricated in the engine through external pipes or tubes. The oil circulating through the respective portions in the engine naturally drops down or returns again to the oil pan through the oil passage.
FIG. 6 shows a sectional view representing an arrangement of a manifold having a general structure, which is applicable to a parallel four cylinder engine, not shown. Four exhaust pipes, not shown, connected to the respective cylinders, are once assembled into two sets of pipe assemblies by means of front manifolds M and then further assembled into one set of pipe assembly by means of a rear manifold, not shown, such one set of pipe assembly being connected to a silencer, not shown. The front manifolds M are arranged approximately in parallel with each other below an oil pan P.
However, in the arrangement of such front manifolds M in a motorcycle, there is a case where sufficient minimum ground clearance and bank angle are not ensured. In order to solve this problem, it is attempted to locate the engine at a relatively high position or make shallow the depth of the oil pan. However, in the case where the engine is located at a high position, a steering stability of the motorcycle will be lowered and in the case where the depth of the oil pan is made shallow, the oil pan does not sufficiently achieve its function. That is, it becomes impossible to ensure a sufficient oil level height of the lubrication oil in the oil pan and the oil pump may absorb an air when the attitude of the motorcycle body changes, thus providing a problem.
In order to solve this problem, there is provided an arrangement such as shown in Japanese Patent Laid-open Publication No. HEI 5-84812 or No. HEI 6-19795, in which the exhaust pipe and the manifolds are arranged in one side of the oil pan to ensure the sufficient depth of the oil pan. However, according to such arrangement, a width dimension of the motorcycle is widened, thus reducing the bank angle, providing also a problem.